Heart failure is the leading cause of combined morbidity and mortality in the United States and other developed industrial nations. It remains an incurable disease process with an estimated two-year mortality of 30-50% for the patients with advanced disease. Although great advances in the treatment for failing heart have been made, the understanding of the molecular mechanism leading to heart failure is still limited. It is evident, however, that severe heart failure is associated with striking decreases in the expression of cardiac specific genes (Razeghi et al., 2002; Hwang et al., 2002; Barrans et al., 2002).
Serum response factor (SRF) is a muscle enriched transcription factor, which plays an important role in the regulation of contractile protein gene expression in mammalian heart. SRF serves as a platform to recruit and interact with other muscle regulatory proteins, such as Nkx-2.5 (Chen et al., 1996) and GATA4 (Sepulveda et al., 1996), and it is also obligate for normal muscle gene transcription. Expression of mutated SRF in transgenic mice can lead to severely dilated cardiomyopathy (Zhang et al., 2001).
SRF is a member of an ancient DNA binding protein superfamily, whose evolutionarily divergent relatives share a highly conserved DNA-binding/dimerization domain of 90 amino acids, termed the MADS box, named after four proteins (MCM1, Agamous, Deficiens, and SRF). The regulatory regions of a number of muscle specific genes such as skeletal, cardiac and smooth muscle α-actin, and other myogenic specified genes contain serum response elements (SRE; an example of which is provided in SEQ ID NO:1), which are required for promoter activity and depend upon SRF for activity (Lee et al., 1992; Li et al., 1997). Mutations that prevent SRF binding severely impair the expression of c-fos, as well as these muscle-restricted promoter (Boxer et al., 1989; Lee et al., 1991). High levels of SRF expression and increased SRF mass appear to coincide with the expression of muscle a actins, noted as early markers for terminal striated and smooth muscle differentiation (Croissant et al., 1996; Belaguli et al., 1997). SRF also serves as a platform to recruit other cardiac enriched transcription factors to activate cardiac specific genes (Belaguli et al., 2000; Chen and Schwartz, 1996). The recent analysis of SRF null mutants revealed an absoulate dependence for SRF for the formation of embryonic cardiogenic mesoderm (Arsenien et al., 1998). Expression of the mutated SRF in transgenic mice can lead to severely dilated cardiomyopathy (Zhang et al., 2001). Taken together, these studies clearly support an obligatory role for SRF as an obligatory myogenic transcription factor.
Apoptosis, or programmed cell death, is an evolutionarily conserved process by which unwanted or damaged cells are removed in order to keep tissue or body homeostasis. When deregulated, apoptosis can result in a number of human diseases including inflammation, cancer and neurodegenerative disease. Apoptosis is associated with the activation of serial caspases in proteolytic cascade after exposure to apoptotic signals (Scarabelli et al., 2002; Scarabelli et al., 2001; Gottlieb et al., 1994). Caspase activation could mediate the cleavage of vital proteins (Sebbagh et al., 2001; Emoto et al., 1995; Moretti et al., 2002) and lead to varied pathogenesis. In fact, caspase 3 activation in apoptotic cultured cells led to SRF cleavage (Drewett et al., 2001; Bertolotto et al., 2000). Recently, heart failure has been associated with cardiac myocyte apoptosis (Kang and Izumo, 2000; Haunstetter and Izumo, 1998; Hirota et al., 1999; Zhang et al., 2000). The loss of functional myocytes via cell apoptosis pathway appears to play an important role in the progression of cardiac failure. With regard to heart failure, the implicit assumption has been that weak activation of the proteolytic cascade associated with caspase leads inexorably toward apoptosis with eventual heart failure arising from myocyte loss (Kang and Izumo, 2000; Haunstetter and Izumo, 1998; Hirota et al., 1999; Narula et al., 1999; Narula et al., 1996; Narula et al., 1998; Narula et al., 1997).